This invention relates to branched polyphenylene-mica composites which can withstand mechanical stress under high temperature conditions.
There is a need for polymeric materials which can withstand mechanical stress under high temperature conditions. Such materials have utility in applications such as in electronic circuit boards and in mechanical seals. Among the polymers which have shown good high temperature properties are branched polyphenylenes. In general, polyphenylenes are polymers composed essentially of carbon and hydrogen in aromatic ring type structures with the rings chemically linked to each other through the ortho, meta and para positions. Such polymers are to be distinguished clearly from other chemically similar phenylene type structures, such as polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfone and other polymers containing the designation "phenylene". Ordinary polyphenylenes generally have been produced by techniques such as acid catalyzed oxidative coupling of the benzene ring in various aromatic compounds and such polyphenylenes possess some degree of high temperature thermal stability, but they are generally linear (para-polyphenylene) polymers which are relatively insoluble and infusable. Polyphenylenes have been produced which do possess certain limited solubility, but these have generally been at number average molecular weights of only about 1000 to 2000. Generally, these low molecular weight polyphenylenes contain only a low degree of branching, that is, they are still relatively linear polymers which contain long linear segments.
The branched polyphenylenes useful in producing superior mica composites are those novel polyphenylenes disclosed by Wennerberg and Wang in U.S. Pat. No. 3,792,099 and produced by the process described in U.S. Pat. Nos. 3,829,518 and 3,798,281, all of which are incorporated by reference herein. These polyphenylenes possess increased solubility over prior art polyphenylenes and excellent thermal stability over a number average molecular weight range from 1000 to over 10,000. Also, small amounts of branched nitropolyphenylene can be incorporated within the composites of this invention. Such nitropolyphenylenes and composites formed therefrom are described in U.S. Pat. No. 3,974,121, which is incorporated by reference herein.